Deep Inelastic Parity

1
Deep Inelastic Parity
Thanks to Paul Souder, Paul Reimer,
Peter Bosted, Xiaochao Zheng,
Kent Paschke, Krishna Kumar
Robert Michaels, JLab

• Electroweak Physics
• Hadronic Physics
• Possibilities with MAD / HMS / SHMS
• New Toroidal Spectrometer

2

• Parity Violating Asymmetry

2

Applications

• Nucleon Structure (e.g. strangeness)
• Nuclear Structure (neutron density)
• Standard Model tests ( )

3
Standard Model Tests

• The standard model of electroweak
  interaction
• Experimentally very successful
• But seems it must break down
  !!
• (issues many
  parameters, origin of mass,
• unification with
  gravity, etc)
• Frontiers
• 1. Higher energy
• 2. Higher precision ? JLab
  parity

p
Q

Moller
DIS
weak
(this talk)
4
Parity Violating Electron DIS
e-
e-
?
Z
X
N
fi(x) are quark distribution functions
For an isoscalar target like 2H, structure
functions largely cancel in the ratio
Provided Q2 1 GeV2 and W2 4 GeV2 and x
0.2 - 0.4
Must measure APV to fractional accuracy better
than 1

• 11 GeV at high luminosity makes very high
  precision feasible
• JLab is uniquely capable of providing beam of
  extraordinary stability
• Systematic control of normalization errors being
  developed at 6 GeV

5
Electron-Quark Phenomenology
V
A
A
V
C1u and C1d will be determined to high precision
by other experiments
C2u and C2d are small and poorly known can be
accessed in PV DIS
New physics such as compositeness, new gauge
bosons
Deviations to C2u and C2d might be fractionally
large
Proposed JLab upgrade experiment will improve
knowledge of 2C2u-C2d by more than a factor of 20
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Physics Implications
7
APV in DIS on 1H
small corrections

• Allows d/u measurement on a single proton!
• Vector quark current! (electron is axial-vector)

• Determine that higher twist is under control
• Determine standard model agreement at low x
• Obtain high precision at high x

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PV DIS and Nucleon Structure

• Analysis assumed control of QCD uncertainties
• Higher twist effects
• Charge Symmetry Violation (CSV)
• d/u at high x
• NuTeV provides perspective
• Result is 3? from theory prediction
• Generated a lively theoretical debate
• Raised very interesting nucleon structure issues
  cannot be addressed by NuTeV
• JLab at 11 GeV offers new opportunities
• PV DIS can address issues directly
• Luminosity and kinematic coverage
• Outstanding opportunities for new discoveries
• Provide confidence in electroweak measurement

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Search for CSV in PV DIS

• u-d mass difference
• electromagnetic effects

• Direct observation of parton-level CSV would be
  very exciting!
• Important implications for high energy collider
  pdfs
• Could explain significant portion of the NuTeV
  anomaly

Sensitivity will be further enhanced if ud falls
off more rapidly than ?u-?d as x ? 1
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Higher Twist Effects
?

• APV sensitive to diquarks ratio of weak to
  electromagnetic charge depends on amount of
  coherence
• If Spin 0 diquarks dominate, likely only 1/Q4
  effects.
• Novel interference terms might contribute
• On the other hand, higher twist effects may
  cancel, so APV may have little dependence on Q2.

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2H Experiment at 11 GeV
E 5.0 GeV 10
?lab 12.5o
60 cm LD2 target
Ibeam 90 µA

• Use both HMS and SHMS to increase solid angle
• 2 MHz DIS rate, p/e 2-3

APV 217 ppm
xBj 0.235, Q2 2.6 GeV2, W2 9.5 GeV2

• Advantages over 6 GeV
• Higher Q2, W2, f(y)
• Lower rate, better p/e
• Better systematics 0.7

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Large Acceptance Concept

• CW 90 µA at 11 GeV
• 40-60 cm liquid H2 and D2 targets
• Luminosity 1038/cm2/s

JLab Upgrade
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6 GeV
50 azimuthal coverage assumed
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• 2 to 3.5 GeV scattered electrons
• 20 to 40 degrees
• Factor of 2 in Q2 range at moderate x
• High statistics at x0.7, with W2

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Cut on 0.6

Large range in Q2 for HT study

High x (0.7) accessible with W24

Large acceptance allows feasible runtime
requests

p/e ratio is not extreme

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d/u at High x
Deuteron analysis has nuclear corrections
APV for the proton has no such corrections
Must simultaneously constrain higher twist effects
The challenge is to get statistical and
systematic errors 2
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d/u Measurements for Proton
(Kent Paschke simulation)
A couple weeks of beam time with toroid
spectrometer
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d/u of Proton
Compare MAD Spectr. to Toroid Spectr.
d/u
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EMC effect in Parity Violation ?
50 days each plot. Solid targets are 1
radiation length.
Cross section data from J. Gomez et.al. PRD 49
(1994) 4348
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PV DIS Program

• Hydrogen and Deuterium targets
• Perhaps heavier nuclei (EMC effect)
• Better than 2 errors
• It is unlikely that any effects are larger than
  10
• x-range 0.25-0.75
• W2 well over 4 GeV2
• Q2 range a factor of 2 for each x point
• (Except x0.7)
• Moderate running times

• With HMS/SHMS search for TeV physics
• With larger solid angle apparatus higher twist,
  CSV, d/u